The consequences of high-flexion postures on arterial wave reflections.

Although central wave reflections are critical for aortic pressure regulation, the control mechanisms involved in humans are understudied. This study investigated the impact of upper- and lower-limb high-flexion postures on central arterial wave reflections. Twenty-two healthy adults (11 females, aged 25 ±  3 years) underwent three randomized and counter-balanced positions to evaluate the effect on central wave reflection: supine legs and arms in the anatomical position; supine two legs bent and arms straight; and supine two arms bent and legs straight. Characteristic impedance, forward and backward pressure waves, and pulse characteristics were measured via the central pressure-flow relationship in the frequency domain at the end of each posture hold. Central diastolic blood pressure increased during arm flexion only (67 ± 9 mmHg vs. 62 ± 9 mmHg; p < 0.01). Central systolic blood pressure, augmentation index, forward wave amplitude, reflected wave amplitude, central wave reflection magnitude, and characteristic impedance were unaffected by varying limb flexion positions (all p > 0.05). Acutely bending the arms and legs did not influence central wave reflections, likely related to a minimal effect of conduit artery bending, versus microvascular involvement, as suggested in previous studies. These findings underscore the importance of identifying the specific vascular regions responsible for wave reflection generation and support the need to refine central pressure augmentation models to accurately localize the dominant sources of wave reflection in humans.